The unsealed search warrants don’t confirm the source of the drug, fentanyl, that led to the 57-year-old singer’s accidental, self-administered overdose last April, according to The Star Tribune.

Investigators found no prescriptions in Prince’s name, however, Dr. Michael Todd Schulenberg told detectives he had written a prescription for oxycodone, which is also an opioid, under the name of long-time Prince associate and drummer Kirk Johnson.

Between April 21 and Sept. 19, 2016, Carver County authorities conducted investigations into Prince’s death with a total of 11 search warrants.